Technical Field
The present invention relates to an adjustable gain power amplifier, a gain adjustment method applied to the adjustable gain power amplifier, and a mobile terminal including the adjustable gain power amplifier, pertaining to the technical field of power amplifiers.
Related Art
With the constant development of wireless communication technologies, various portable wireless communication devices have been widely applied. A power amplifier is an indispensable circuit module in a wireless communication device, and is mainly responsible for amplifying a modulated radio frequency signal to a particular power value and transmitting the amplified signal by using an antenna, so that a base station nearby receives the amplified signal. An operating band of a wireless terminal covers various mobile communication standards such as Wideband Code Division Multiple Access (WCDMA) and Time Division-Synchronous Code Division Multiple Access (TD-SCDMA). Regardless of which communication standard is used, a mobile terminal usually needs to adjust a transmit power of a power amplifier according to a distance between the mobile terminal and a base station.
When a wireless communication terminal is far away from a receiving base station, a power amplifier needs to transmit a signal by using a relatively high transmit power, so that the signal still has sufficient strength and can be received and recognized by the base station when arriving at the base station. In contrast, when the wireless communication terminal is near the base station, the power amplifier only needs to transmit the signal by using a relatively low power. Therefore, it is required during design to enable a radio frequency power amplifier to switch between several power (gain) modes. A common power amplifier includes two power modes, namely, a high power mode and a low power mode. A relatively high gain is required in the high power mode and a relatively low gain is required in the low power mode, so that the power amplifier realizes an output of a large dynamic range.
FIG. 1 is a circuit diagram of a common power amplifier in the prior art. The circuit includes two independent amplification paths: a high power mode amplification path and a low power mode amplification path. The two paths share one input and one output. When the power amplifier works in the high power mode, a switch 101 and a switch 102 are closed, and a switch 103 and a switch 104 are open. Moreover, a biasing circuit 105 provides a biasing voltage to an amplification circuit 106, and a biasing voltage of an amplification circuit 107 is cut off. In contrast, when the power amplifier works in the low power mode, the switch 103 and the switch 104 are closed, and the switch 101 and the switch 102 are open. Moreover, the biasing circuit 105 provides a biasing voltage to the amplification circuit 107, and a biasing voltage of the amplification circuit 106 is cut off. For another example, Chinese Utility Model Patent No. ZL 200920055959.X discloses a high and low power combining circuit for a radio frequency power amplifier. The circuit also uses two power modes. Three switches in the circuit are controlled by using a voltage to perform power switching on a radio frequency signal, so as to control a cut-off of an amplifier and switch between a high power and a low power. However, in all the foregoing power amplifiers, the high power mode and the low power mode are independently designed. Although the performance can be optimized, the overall circuit design is relatively complex, requiring excessive resources and increasing production costs. More importantly, limited by the gallium arsenide (GaAs) process, it is difficult to integrate switches required on a radio frequency path.